It is well known that DSL technology is not compatible with POTS devices such as a telephone or fax apparatus concurrently using the same wiring. In order to guarantee a reliable and stable DSL service, a POTS splitter, i.e. a dedicated device filtering the POTS frequency band from the frequency bands used for upstream and downstream DSL service, is installed. Such POTS splitter has to be installed centrally or on each POTS device at the customer premises. The installation of such POTS splitter(s) is often done by the end-user.
Absence or improper installation of a POTS splitter leads to interference between POTS and DSL signals, resulting in DSL service degradation or service instability through transmission errors and resynchronizations. A DSL operator faced with service degradation or instability on a particular DSL line must determine the cause of the service degradation in order to be able to repair the service. In addition, the DSL operator must determine the responsible party of the service degradation in order to be able to charge the intervention or reparation costs to that party. Absence or improper installation of a POTS splitter may result in the end-user being charged for the intervention, whereas service degradation resulting from impairments in the DSL operator's domain are paid for by the DSL operator.
Several tools and mechanisms have been developed already to assist DSL operators in detecting the absence or improper installation of POTS splitters, but these existing methods are slow, complex, have limited reliability and/or require the presence of the customer as will be explained in the following paragraphs.
A straightforward solution consists in dispatching a technician to the customer premises in order to verify if all POTS devices have been configured properly with POTS splitters. Such solution is expensive and time consuming, and access is required to the customer premises, i.e. the end-user's home or office.
An alternative solution, the so-called time segmentation algorithm, relies on detection of parameter changes resulting from a transition between the on-hook and off-hook states of a telephone. In the absence of a POTS splitter, such a transition exhibits an impedance change that is so severe that the DSL line has to resynchronize. After the transition between on-hook and off-hook state, the operational line parameters of the DSL line, like bit rate, noise margin, signal-to-noise ratio or SNR, etc. have changed completely. By monitoring the parameter variations at the transition from on-hook to off-hook state, the time segmentation algorithm can detect absence of a POTS splitter.
The time segmentation algorithm is disadvantageous in that it requires at least one phone call to happen on the monitored line. Detection of the absence of a POTS splitter consequently is slow because typical monitoring periods of 1 day are required in order to capture a phone call. Moreover, the end-user must be present at the customer premises to pick up the phone.
The time-segmentation algorithm may be improved by inducing a phone event, e.g. sending a ringing signal in the POTS frequency band, while monitoring the DSL operational line parameter changes. The ringing signal however may be insufficient to cause detectable parameter variations. The best results are obtained when the phone transits from on-hook to off-hook status, but this so called interactive test requires presence of the end-user at the customer premises to pick up the phone. This improved time-segmentation algorithm is further disadvantageous in that it requires access to both DSL and telephone switch infrastructure. This involves complex Operation Support System (OSS) integration.
Another existing solution relies on detection of leakage of signal power from the upstream DSL band into the downstream DSL band as a result of inter-modulation induced by a POTS device in the absence of a POTS splitter. The inter-modulation phenomenon is not linear. As a result, a small variation in the upstream transmitted power may result in large variation of for instance the SNR in the downstream band. This existing test therefore consist in varying the upstream transmitted power and monitoring the operational line parameter changes in the downstream band.
Although no access is required to POTS equipment and the presence of a person at the customer premises is no longer needed, this method still involves complex OSS integration because a change in the line configuration parameters is needed. The test based on inter-modulation is further poorly reliable because not all POTS devices induce an inter-modulation level that is sufficiently to make POTS splitter absence detectable. Further, the test is plagued by false positive detection because other impairments, like for instance oxidized contacts, can also create inter-modulation.
It is an objective of the present invention to provide a device and method for detection of absence of a POTS splitter on a DSL line that resolves the above mentioned shortcomings of existing solutions. More precisely, it is an objective of the present invention to disclose a device and method that detects the absence of a POTS splitter without dispatching technicians, without requiring lengthy monitoring periods, without requiring presence of a human being at the customer premises, without complex OSS integration involving access to POTS equipment, and with improved reliability.